Contact construction



Nov. 23, 1943. A H. POWELL coNTAcT CONSTRUCTION Filed March 21, 1 942,.hmm.. .mmm

Nl N Inventor-u Alric H. Powell, b5

His Attornee.

Patented Nov. 23, 1943 CONTACT CONSTRUCTION Alric H. Powell, Yeadon,Pa., assignor to General Electric Company, a corporation of New YorkApplication March 21, 1942, Serial No. 435,648

Claims.

My invention relates to a Contact construction for an electric circuitinterrupting device, such as a fuse or a switch, and more particularlyto a Contact construction for a fuse of the expulsion type.Specifically, my invention is an improvement on the arrangementdisclosed in Williams Patent 2,043,024, assigned to the same assignee asthe present application.

Expulsion fuses have been used quite extensively for protectinghigh-voltage circuits and machinery interconnected in such high-voltagecircuits. In expulsion fuses of the type disclosed in theabove-mentioned patent, the lower fuse terminal and the remainingportions of the fuse link are expelled from the fuse casing upon blowingof the fuse. In order that the lower fuse terminal may readily beexpelled, it would be desirable to provide a lower Contact constructionwhich, upon blowing of the fuse, will permit ready separation of thecontacts. such a Contact is constructed to be readily expelled from thefuse casingv upon blowing of the fuse element, it may be at the sacriceof a good contact during the unblown condition of the fuse, resulting inhigh operating temperatures which may be undesirable.

Accordingly, it is an object of my invention to provide a new andimproved contact construction for an electric circuit interruptingdevice which is simple in construction and eilicient in operation.

It is another object of my invention to provide a contact constructionfor an expulsion fuse device which not only is readily expelled from thefuse casing upon blowing of the fusible element but which provides anexcellent current-carrying Contact capable of operating at lowtemperatures when carrying high currents during the unblown condition ofsaid fuse.

Further objects and advantages of my invention will become apparent asthe following description proceeds and the features of novelty whichcharacterize my invention will be pointed out with particularity in theclaims annexed to and forming a part of this specication.

For a better understanding of my invention, reference may be had to theaccompanying drawing in which Fig. 1 is a view partly in section of anexpulsion fuse device embodying my invention and illustrated in theunblown condition;

Iig. 2 is a. similar sectional view at the instant of rupture of thefuse link; Fig. 3 is a sectional View taken on line 3-3 of Fig. l; Fig.4 is an exploded view of the movable contact portion of However, if'

my invention; and Fig. 5 is a force diagram to aid in the understandingof my invention.

Although my improved Contact construction may be applicable to manyforms of circuit-interrupting devices, I have specically illustrated itin the drawing as applied to an expulsion fuse which, except for theContact construction, is substantially identical to that disclosed inthe above-mentioned Williams patent. Referring now to Figs. l and 2 ofthe drawing, III indicates a tube of insulating material which forms thehousing of an expulsion fuse. Conducting ferrules or terminals II and I2are secured to each end of tube Ill as by crimping indicated at I3.Ferrules II and I2 are preferably made of a metal having highconductivity and are adapted to Contact with terminals connected in anelectric circuit. In order to complete the circuit between ferrules IIand I2, I provide a fuse link I4 which consists of a flexible conductorI5, a fusible link I6, and a strain wire Il, all located within the fusecasing comprising tube |01 and ferrules II and I2.

The upper end of flexible cable Or conductor I5 terminates in a swagedterminal I8 which is in conducting relationship with the lower end offusible element I6 preferably made of one of the well-known fusibleelements which is readily fusible on the passage of electric currenttherethrough and which has a relatively low specific resistance. Theother end of fusible element I6 is connected to a terminal I9 which isconnected to a Contact 20 by means of a bolt 2I. Contact 20 rests uponthe top of tube I0 and is in engagement with the ferrule I I to completethe connection between fuse link I4 and the upper fuse contactcomprising ferrule I'I. If desired, the fusible element I6 may becompletely surrounded by a tube of insulating material' 22 as disclosedin the above-mentioned prior patent.

If the fusible element I6 cannot withstand the tension applied to fuselink I4 as is described in greater detail hereinafter, it may bedesirable to provide a strain wire I'I in parallel with fuse link I6.The lower end of strain wire I'I may be electrically connected to swagedterminal I8 if desired or, in the event of a fuse device for carryingvery low currents, the lower end of strain wire I'I may be insulatedfrom terminal I8 by insulating member 23 as disclosed and claimed in theabove-mentioned Williams patent. The upper end of the fuse casing ispreferably closed by an end cap 24 soldered within the top of ferrule IIto form a waterproof joint.

The arrangement described heretofore is not my invention but isdisclosed and claimed in the above-mentioned Williams patent and isincluded herein merely to aid in understanding the contact constructionof my invention to be described hereinafter.

The lower end of flexible conductor I5 of fuse link IfI is electricallyconnected to ferrule I2 through a high pressure contact with which myAinvention is specifically concerned. Ferrule I2, which is cylindrical inconstruction, forms the stationary annular portion of the pressurecontact and is adapted to be engaged by a collapsible portion of thecontact generally indicated at comprising a toggle including a pluralityof punchings 25, 21, 28, and 29. The punchings 26 and 21 have anembossed portion 32 which may be inserted in opening 3l of member 23 toact as the pivotal support for the member 23.

The three members 26, 21, and 28 may be held in assembled relationshipby a suitable pin 34 passing through the openings 32 in members 26 and21 and the opening 33 in member 25 as indicated in Fig. fl. Flexibleconductor 5 is preferably brazed or welded to member or shoe 29 or, if

Y tact portion 25, each of the members 223, 21, and

23 being provided with a cooperating notch or groove 36 to accommodatespring 35. It will be obvious from Fig. l that exible cable I5 holds theembossed portions 3Q of members 25 and 21 in a iixed position so thateffectively members 26, 21, and are pivoted about a xed point referredto as 39 and spring means 35 biases the contacting portions of members23, 21, and 28 which act as a toggle with the pivot point Sil as theknee into firm engagement with the interior surface of ferrule I2 asindicated at X, Y, and Z, respectively, in Fig. 3.

The collapsible contact portion 25 is constructed so that a relativelysmall force produced by spring means 35 is converted into a high contactpressure as may be best understood by reference to Fig. 5 where thecontact elements are schematically shown with the corresponding partsthereof designated by the same reference numerals as in Figs. 1 to Ll.The point 30 of Fig. 5 is assumed to be a fixed pivot such as embossedportions 3G of Fig. 4 held in such position by means of cable I5. Themembers 21 and 28 are indicated as a single line making an angle 0 withthe horizontal. The force F1 applied intermediate the ends of members 21and 28 represents the portion of the spring force applied to each memberwhich may be assumed to be equally applied to the members of thecollapsible contact portion 25. Neglecting the friction factor betweenthe end of member 28 and the interior surface of ferrule I2, the onlycomponent of force in addition to force F1 effective to cause rotationabout pivot is the force F2 representing the contact pressure betweenthe member 28 and ferrule I2. It will be obvious from Fig. 5 and thefundamental relationship that the sum of the moments about any point areequal to zero that'the following relationship exists when expressing themoments about point 30 and the friction force between the collapsiblecontact 25 and ferrule I2 is neglected.

F2b sin 0=F1a (l) which in terms of the contact pressure F2 may beexpressed as follows:

F1a F2b sin 0 (2) For very small angles of 6 in the neighborhood of tendegrees or so, it is obvious that the contact pressure F2 may be ve orsix times the spring force F1 applied to any one member 2B, 21, or 28,and, consequently, with such high contact pressure, a very efficientcontact is provided. The members 26, 21, and 28 have suiicient massreadily to carry away the heat from the points of contact X, Y, and Z ofFig. 3 and, consequently, provide a contact structure which operates atmuch lower temperatures than was heretofore possible.

Upon rupture of the fuse link I4 as indicated at 38 in Fig. 2, theflexible conductor I5 no longer holds embossed portions 30 as a xedpivot to support the collapsible contact portion 25 and spring means 35tends to rotate the members 26, 21, and 28 about the points of contactX, Y, and Z of Fig. 3. As soon as this happens, the contact pressure isremoved by collapsing of contact portion 25 in the manner indicated inFig, 2 and the entire contact assembly is forced out of the fuse casingunder the force of spring 35 and the expulsion action of the fusedevice. Because of the collapsible contact portion 25, a much more rapidremoval of the contact and remaining portions of the fuse link ispossible than with prior-art constructions which usually required largesliding surfaces to satisfactorily carry the current and which tended tocorrode and to become otherwise difcult to move.

The lower end of ferrule I2 is preferably closed by a frangible disk ora flexible disk 31 formed of Celluloid or the like, which is readilyforced out of the lower end of the fuse casing upon rupture of thefusible element. Disk 31 not only serves to keep insects, moisture, anddust from entering the lower end of the fuse casing but also serves as atarget in so far as indicating whether or not the fuse device hasoperated.

The operation of the contact structure will be obvious in View of thedetailed description included above.

From the foregoing, it may be seen that, by means of my improvedfrictional contact construction, I have provided a Contact which willoperate more efficiently and at lower temperatures than arrangementsheretofore. In addition, the construction is much more positive incompletely removing the contact portion and the remaining portions ofthe fuse link from the fuse casing upon rupture of the fusible element.

While I have shown and described my invention in considerable detail, Ido not desire to be limited to the exact arrangement shown but seek tocover in the appended claims all those modications that fall within thetrue spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. In combination with a circuit-interrupting device, a pressure contactcomprising a stationary contact portion and a movable cooperatingcontact portion, said movable contact portion comprising a plurality ofpivotally related elements forming a collapsible member which may bebiased into good current-carrying engagement with said stationarycontact portion, means for causing relative movement between saidcontact portions, and means normally opposing the operation of saidlast-mentioned means to cause said collapsible member to be biased intocontacting engagement with said stationary conta-ct portion.

2. In combination with a fuse device including a tubular casing having astationary annular contact at one end thereof, a fuse link in saidcasing, a plurality of pivotally related elements JorrninU a collapsiblemember fastened to one end of said fuse link and arranged to form amovable contact adapted to cooperate with said annular contact, andmeans including said fuse link for biasing said movable contact againstsaid stationary annular contact at high pressure, said last-mentionedmeans also including a spring for causing collapse of said movablecontact to release the pressure between said contacts and permitrelative high-speed separation of said contacts upon rupture of saidfuse link.

3. In combination with an expulsion fuse device, a tubular casing, apair of terminals one at each end of said casing, a fuse link in saidcasing, means for connecting one end of said fuse link with one of saidterminals, a collapsible contact connected with the other end or" saidfuse link and adapted to be biased into engagement with the other ofsaid terminals, and means including a spring for tensioning said fuselink and forcing said collapsible contact into engagement with saidother terminal, said collapsible contact being constructed to multiplythe spring force applied thereto to produce a high pressure contact withsaid other terminal which is readily released upon rupture of said fuselink to permit high-speed separation of said contacts and completeexpulsion from said casing of said collapsible contact by the expulsionaction of said fuse device.

fl. A fuse comprising an annular contact, a fuse link, a piurality ofmembers pivotally related so as to form a toggle having the knee thereofconnected to said fuse link and the ends thereof adapted to engage saidannular contact, and means including a spring for engaging said toggleintermediate the knee and the ends thereof for forcing the ends of saidtoggle into high pressure engagement with said annular contact toproduce an efficient current path from said fuse link to said annularcontact.

5. In combination with an expulsion fuse device, a tubular casing, apair of terminals one at each end of said casing, a fuse link in saidcasing, means for connecting one end of said fuse link with one of saidterminals, a collapsible contact including a plurality of pivotedmembers connected with the other end of said fuse link and adapted to bebiased into engagement with the other of said terminals, and acompression spring interposed between one end of said casing and saidpivoted members for tensioning said fuse link and forcing saidcollapsible contact into engagement with said other terminal, saidcollapsible contact being constructed to multiply the spring forceapplied thereto to produce a high pressure contact with said otherterminal which is readily released upon rupture of said fuse link topermit high-speed separation of said contacts and complete expulsionfrom said casing of said collapsible Contact by the expulsion action ofsaid fuse device.

ALRIC H. POWELL.

